Open Loop: bundle unit = preset {loops, prompts, skills}

[suleimansh]

Part of #204 (first slice). Keystone.

Introduce the composable unit that ties together the three data types we already ship separately:

• loops (meta prompts)
• prompts (frontmatter + md body, via loadPromptsFrom)
• skills (framing personas + llms.txt pointer)

A preset is a directory of these. It can be selected and composed (presets-of-presets falls out of composability).

Out of scope for this issue: marketplace/registry, framework-* detection (skipped for MVP per Rom).